The emergency services were called to the westbound carriageway between J26 near ChainBar and J25 near Brighouse at around 3pm.
A lane was closed to allow Yorkshire Ambulance to attend the scene.
The incident caused long queues for around seven miles, adding at least 30 minutes onto journey times between J26 at Bradford and J28 near Leeds.
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Highways England say all lanes have now re-opened and the scene is clear, but delays are expected into Friday evening.